The challenges of solar governance in temperate-climate cities: the case of Vienna

Climate change has made urban heat a source of concern in temperate-climate cities that, until recently, have not viewed heat stress as a major urban challenge. While heat mitigation policies put an emphasis on outdoor shade during summer, its provision can sometimes be in conflict with established regulations on winter solar access indoors and outdoors. Such conflicts are now addressed, if at all, mostly through an ad-hoc intuitive assessment of designers and not by following a clear methodology for resolving contradicting urban climatic goals.

The study addresses this inherent conundrum of solar access by building a framework of distributive justice that differentiates spatial entities for their perceived need for solar governance. We argue that measurable climatic metrics alone cannot resolve this conundrum since an optimal year-long “average” of negative and positive solar exposure would normally produce non-optimal conditions during winter and summer alike. Consequently, the governance of solar access in cities has to rely also on context specific societal interests, considering the subjective preferences of a variety of stakeholders, including city planners and residents. For example, a city may decide that winter solar access is far more important than solar protection in playgrounds and, at the same time, highly prioritise sidewalk summer shade over indoor winter illumination.

Taking Vienna as a case study, we set out to identify the spatial entities that local stakeholders consider to be a relevant reference framework to solar access claims. Using the analysis of official regulatory documents, expert interviews, and open citizen discussions, we were able to identify a set of spatial units that were considered as requiring solar governance, such as residential apartments, key-way connections, transport stops, playgrounds, and public squares. The resulting spatial solar access claims were modelled on a typical site as a negotiation platform for resolving the solar conflicts.